In a typical interfolding system, a web is cut into a series of successive sheets on a bed roll, which includes vacuum ports that maintain the leading edge of each sheet in engagement with the surface of the bed roll. The sheets are fed from the bed roll to a series of stripper fingers, and guides are located adjacent the stripper fingers to form a sheet supply passage that leads to a nip formed by a pair of retard rolls. A pick roll forms a nip with the bed roll, and engages the trailing end of each sheet to lift the trailing end of the sheet off the bed roll. The speed of rotation of the retard roll is slower than the rate of advancement of the sheets in the supply passage, which advances the stream of sheets in the discharge passage at a rate slower than the speed of advancement of the sheet on the bed roll. In this manner, when the trailing end of a downstream sheet is lifted off the bed roll by the pick roll, the leading end of the successive upstream sheet is advanced by the bed roll past the trailing end of the downstream sheet, which causes the successive sheets to overlap or “shingle” within the supply passage. The retard rolls supply the stream of shingled or overlapped sheets to the folding rolls, which interfold the sheets to form an interfolded stack of sheets.
Due to engagement of the trailing portion of each sheet with the pick roll as the sheet is discharged from the bed roll, the trailing portion of each sheet bulges or bubbles outwardly as the sheet is moved into the stream of shingled or overlapped sheets in the sheet supply passage en route to the retard rolls. The bulge or bubble in each sheet is controlled by a transverse control bar that is positioned below the pick roll and outwardly of the stripper fingers, above the guides that cooperate with the stripper fingers to form the sheet supply passage.
A system such as this functions well at certain speeds, e.g. up to approximately 350 sheets per minute. It has been found that, at higher speeds of operation, the system experiences certain adverse effects that result in unsatisfactory performance, particularly in the sheet overlapping area. Specifically, it is believed that, when the trailing portion of a sheet is moved outwardly by operation of the pick roll to form the bubble or bulge in the trailing portion of the sheet, the leading portion of the successive upstream sheet is drawn outwardly along with the bubble or bulge in the trailing area of the downstream sheet. Such outward movement of the leading portion of the upstream sheet causes the leading edge of the upstream sheet to strike the downstream sheet, which causes misalignment between the sheets and inaccurate positioning between the trailing edge of the downstream sheet and the leading edge of the adjacent upstream sheet.
The object of the present invention is to overcome the above-described problem to enable operation of the interfolder at high speeds.
In accordance with the present invention, pressurized air is introduced between the trailing area of the downstream sheet and the leading area of the successive upstream sheet, to prevent the leading portion of the upstream sheet from being drawn outwardly along with the bubble or bulge in the trailing area of the downstream sheet. The pressurized air is introduced using a transversely extending air supply tube or pipe, which is positioned below the pick roll and above the transverse control bar. The air supply tube or pipe includes openings, such as slots or holes, that are oriented so as to direct a flow of pressurized air below the pick roll and above the transverse control bar, into a volume within which is formed the bubble or bulge between the trailing end area of the downstream sheet and the leading end area of the upstream sheet. The pressurized air functions to counteract the vacuum that otherwise results from the outward movement of the trailing portion of the downstream sheet after it is released from the bed roll and moves outwardly by operation of the pick roll to form the bubble or bulge in the trailing end area of the downstream sheet. The introduction of pressurized air into the volume thus maintains the leading end area of the upstream sheet in engagement with the stripper fingers or other structure that is used to guide the overlapped sheets through the sheet supply passage toward the retard rolls, downstream of the bed roll. At the same time, the pressurized air functions to force the trailing area of the downstream sheet outwardly against the transverse control bar, to ensure adequate separation between the trailing end area of the downstream sheet and the leading end area of the upstream sheet and to enable the leading edge of the upstream sheet to be fed from the bed roll into the volume without interference from the trailing end of the downstream sheet.
The pressurized air is constantly directed toward the volume within which the leading end of the upstream sheet is supplied. The pressurized air impinges on the downstream sheet, and may be directed into the volume via grooves formed in the pick roll. When the trailing end of the downstream sheet is engaged with the pick roll, typically via a series of laterally spaced vacuum ports that open onto the surface of the pick roll, the pressurized air passes into the volume by separations formed between the downstream sheet and the surface of the pick roll between the vacuum ports, in addition to the grooves in the surface of the pick roll. Once the trailing end of the downstream sheet is released from engagement with the pick roll, the pressurized air is supplied into the volume through a space defined between the trailing end of the sheet and the surface of the pick roll as the sheet is advanced downstream relative to the pick roll.
The invention contemplates a sheet supply system for use with an interfolder in accordance with the foregoing summary, as well as a method of supplying successive overlapped sheets to an interfolder, also in accordance with the foregoing summary.
Various other features, objects and advantages of the invention will be made apparent from the following detailed description taken together with the drawings.